Bylaws as to the use of roads
(1) Subject … to the provisions of this Act or of any other enactment in respect of any of the matters referred to in this subsection, any Minister of the Crown in respect of any roads under his control, or any local authority in respect of any roads under its control, may from time to time make bylaws for any of the following purposes:
...
(i) Prohibiting or restricting absolutely or conditionally any specified class of traffic (whether heavy traffic or not), or any specified motor vehicle or class of motor vehicle which by reason of its size or nature or the nature of the goods carried is unsuitable for use on any road or roads specified in the bylaw:
...
(2) Any bylaws made under this section may apply generally to all roads under the care, control, or management of the Minister or local authority making the bylaws, or to any specified road, or to any specified part or parts thereof, and may apply to all vehicles or traffic or to any parts thereof, and may apply to all vehicles or traffic or to any specified class or classes of vehicles or traffic, and may operate at any time or at any specified time or times.

My concern is that the purpose of the empowering provision is to address the (un)suitability of the vehicle on the road. Typically this would mean banning heavy vehicle (ie, the reverse of the 3,500 kg restriction!) from roads that are not able to cope with them or prohibiting long or wide trucks from narrow streets. The temporal restriction of the ban means the Council accepts that the vehicles are not unsuitable, indicating they are using this provision for a different purpose, namely prohibiting boy-racers. Whether or not that is a sensible purpose, it is an ulterior one beyond the scope of the legislation and therefore unlawful.
Unlawful! And that's even without considering the repugnance of the bylaw ban to the common law right to pass and repass on roads and the freedom of movement protections in the Bill of Rights. They further augment this conclusion, particularly as the Bill of Rights would require an ambiguity about the purpose of the provision to be resolved in favour freedom of movement.
UPDATE (27/6/2007):
> CCC "Street Racing Bylaw Control" (& Legal Opinion)
> CCC "Commencement of Special Order Proceedings to make The Christchurch City Traffic and Parking Alteration Bylaw 2001"
> CCC "Confirmation of Special Order Proceedings - Christchurch City Traffic and Parking Alteration Bylaw 2001"
Aha!
Someone who has done some further digging has alerted me to the fact that Christchurch City actually agreed with me that the bylaw cannot be made under s 72 of the Transport Act 1972. Instead, they relied a different power, s684(30) of the Local Government Act 1974:

s684 Subject-matter of bylaws
(1)Without limiting the power to make bylaws conferred on the council by any other provision of this Act or by any other Act, the council may from time to time make such bylaws as it thinks fit for all or any of the following purposes:
...
Roads
(13) Concerning roads and cycle tracks and the use thereof, and the construction of anything upon, over, or under a road or cycle track:
...
Recreation and Community Development
(30) Regulating the use of any reserve, recreation ground, or other land, and any public building or public place vested in the council or under the control of the council:

Notably the Council lawyers decided that the specific empowering provisions addressing the regulation of traffic and the use of road (Transport Act, s72 and LGA74, s684(13)) could not be used. Instead they purported to rely on a more general provision allowing the bylaws for the purpose of "regulating the use ... of any ... public place vested in the council" - on the basis that roads are vested in the Council under ss 130 & 131 of the LGA74.
Again, cunning but - in my view - unlawful. There's no doubt in my mind that the empowering provision and surrounding statutory scheme mean that that provision cannot be used to regulate traffic on roads. For example:
- the more specific provisions addressing the regulation of roads (which do not apply) trump the more general provisions;
- s684(30) must be read in the light of the heading above it: "Recreation and Community Development"; it's more about regulating sports grounds and the like, not roads, which are addressed in s684(13) and elsewhere.
The Council has tried to refashion a regulatory tool designed for one purpose to address a completely different mischief. Again, the bylaw is in my view ultra vires the empowering provision and/or adopted for an ulterior purpose!
As an aside, s684(30) has been repealed. The equivalent provision in s146 of the LGA2002 provides:

Without limiting section 145, a territorial authority may make bylaws for its district for the purposes—
...
(b) of managing, regulating against, or protecting from, damage, misuse, or loss, or for preventing the use of, the land, structures, or infrastructure associated with 1 or more of the following:
(i) water races:
(ii) water supply:
(iii) wastewater, drainage, and sanitation:
(iv) land drainage:
(v) cemeteries:
(vi) reserves, recreation grounds, or other land under the control of the territorial authority:

And the more general empowering provisions in s 145 LGA 2002 provide:

s145 General bylaw-making power for territorial authorities
A territorial authority may make bylaws for its district for 1 or more of the following purposes:
(a) protecting the public from nuisance:
(b) protecting, promoting, and maintaining public health and safety:
(c) minimising the potential for offensive behaviour in public places.

Although the LGA74 power has been repealed the bylaws is deemed under s193 LGA 2002 to be made under the LGA 2002. Now, I think this means the Council must rely on the new powers in the LGA 2002 when amending the bylaw.
Now, in my view, reliance on s146 creates the same problems as arose under s684(30). Reliance on s145 is possible (to the extent that it relates of nuisance and/or public safety), but I think is also unlawful: again, for the reason that the specific empowering provisions relating to roads and traffic - which aren't available - circumscribe the general powers to regulate.
The other complication arising from purported reliance on the LG Acts rather than the Transport Act is that it probably means the Police have no power to issue infringement notices for any breach. There is (presently) no power under the LGA 2002 to issue infringement notices for breaches of bylaws (unless the Minister of Internal Affairs so orders for particular bylaws - not applicable here). The provisions in the Land Transport Act 1998 (ss 2 "infringement offence" and 138) and Transport Act 1962 (Schedule 2) only allow infringement notices in certain circumstances, only for breaches of "any provision of any bylaw involving the use of vehicles" this is doubtful given the bylaw, according to its stated empowering provision, is about the regulation of the use of public places, not the use of vehicles.
I'm not sure if Manukau City took the same view and relied on the LGA provisions rather than s72 of the Transport Act, but I'm trying to find out.
UPDATE (28/6/2007):
> ThePress: "Expert: Templeton boy-racer ban unlawful"

Course Outline

"From time to time ... lawyers and judges have tried to define what constitutes fairness. Like defining an elephant, it is not easy to do, although fairness in practice has the elephantine quality of being easy to recognise. As a result of these efforts a word in common usage has acquired the trappings of legalism: 'acting fairly' has become 'acting in accordance with the rules of natural justice', and on occasion has been dressed up with Latin tags. This phrase in my opinion serves no useful purpose and in recent years it has encouraged lawyers to try to put those who hold inquiries into legal straitjackets.... For the purposes of my judgment I intend to ask myself this simple question: did the [decision-maker] act fairly towards the plaintiff?"

This course examines the elephantine concept of fairness in the law, along with other contemporary legal issues.